Currently, when no id of an element is entered, the "<id>" label is displayed in the node.

This caused issues during usability testing. User for some reason thought the "<>" characters have some meaning and edited the value to "<myId>" and then was confused why he sees "&lt" and "&gt" sequences in the XML.

Note that sapphire does not have placeholders, so this is just a workaround (when id is null, the <id> text is shown).

This approach is has also disadvantage that if user double click the <id> of empty id, presses an arrow and then enter, the whole <id> value originally meant as a placeholder is now the literal value of the property.

I suggest keeping the place for label just empty. User can be still notified by a validation marker and the label inline editor is still accessible by double click.